This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A287119 #21 Jun 26 2017 05:10:51 %S A287119 8569,39689,321265,430199,564719,585311,608399,7056721,11255201, %T A287119 17966519,18996769,74775791,75669551,136209151,321239359,446660929, %U A287119 547674049,866223359,1068433631,1227804929,1291695119,2315403649,2585930689,7229159729,7809974369,8117634239 %N A287119 Squarefree composite numbers n such that p^2 - 1 divides n^2 - 1 for every prime p dividing n. %C A287119 Such numbers are odd and have at least three prime factors. %C A287119 Problem: are there infinitely many such numbers? %H A287119 Giovanni Resta, <a href="/A287119/b287119.txt">Table of n, a(n) for n = 1..50</a> %o A287119 (PARI) isok(n) = {if (issquarefree(n) && !isprime(n), my(f = factor(n)); for (k=1, #f~, if ((n^2-1) % (f[k,1]^2-1), return (0));); return (1););} \\ _Michel Marcus_, May 20 2017 %Y A287119 Cf. A002997, A006972, A175530, A175531. %Y A287119 Subsequence of A120944. %K A287119 nonn %O A287119 1,1 %A A287119 _Thomas Ordowski_, May 20 2017 %E A287119 More terms from _Michel Marcus_, May 20 2017 %E A287119 a(14)-a(26) from _Giovanni Resta_, May 20 2017